constancy vs sincerity

constancy

noun
  • The quality of being constant; steadiness or faithfulness in action, affections, purpose, etc. 

  • An unchanging quality or characteristic of a person or thing. 

sincerity

noun
  • The quality or state of being sincere 

How often have the words constancy and sincerity occurred in a corpus of books? (source: Google Ngram Viewer )